It has been well known to use key tops made of translucent resin for input keys or buttons of the input unit of electronic equipment including various types of terminal equipment or mobile communication equipment.
There are two types of such input keys having translucent resin key tops. Input keys of the first type have pressure applicators made of silicon rubber, while those of the other type have key tops integrated with a film as disclosed in Japanese Patent Application laid open No. 2003-217396.
FIG. 1 is a cross section diagram showing conventional input keys in the first type. As shown in FIG. 1, input keys 31 are formed by gluing key tops 32 made of translucent resin onto the upper surface of a keypad 33 with a translucent adhesive. The keypad 33 is formed of a translucent silicon rubber sheet and provided with protruding pressure applicators 33a in positions opposite to the respective key tops 32. The input keys 31 are mounted on a housing 38 so that the key tops 32 are exposed to outside. In the housing 38, key switches 37 are arranged on a substrate 34 so as to be opposite to the respective pressure applicators 33a. A reinforcing board 35 supports the substrate 34. The pressing of the key top 32 presses the key switch 37 through the pressure applicator 33a, thereby bringing the key switch 37 in contact with an electrode (not shown) on the substrate 34. Thus, key input is provided. The light from a light source 36 on the substrate 34 transmits through the translucent keypad 33, and illuminates the keys to make letters, symbols, etc. printed on the under surfaces of the key tops 32 visible from outside through the key tops 32.
In this construction, however, the silicon rubber keypad 33 having the pressure applicators 33a is bonded to the key tops 32, which consequently necessitates an increase in thickness. Besides, since silicon rubber assumes a milk-white color even though it is translucent, the transmission decreases due to lower brightness or luminance.
In order to solve such problems, there have been proposed techniques in which key tops are integrated with a film as for example disclosed in Japanese Patent Application laid open No. 2003-217396.
FIG. 2 is a cross section diagram showing the construction of a conventional key sheet formed of key tops integrated with a film. According to the conventional technique, as shown in FIG. 2, a key sheet 41 is formed of a 50 to 250-□m thick resin film 43 having convexities and key tops 42 made of a resin member integrated with the back side of the resin film 43. The respective key tops 42 are provided with protruding pressure applicators 42a. 
With this construction, the increase of thickness can be prevented as compared to the conventional input keys of the first type having the pressure applicators made of silicon rubber. However, in the case of keys integrated with a film described as in Japanese Patent Application laid open No. 2003-217396, key tops have pressure applicators thereunder. Accordingly, in order that the prints of letters, symbols, etc. are provided on the upper surface of the key tops and also fingers will not touch them, the key tops need to be covered with a film having the prints on it. Such film causes a decrease in the light transmission of the entire key sheet. In addition, because the film having the prints on it is prepared in advance, there are limitations to prints and decorations.